Earnings Per Common Share - Basic Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		6 Months Ended
		Oct. 31, 2020	Oct. 31, 2019	Oct. 31, 2020	Oct. 31, 2019
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total (in usd per share)	[1]	$ 0.02	$ 0.06	$ 0.08	$ 0.09
Basic weighted average common shares outstanding (in shares)		32,489	31,609	32,414	31,440
Class A Common Shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Distributed earnings (in usd per share)		$ 0.11	$ 0.11	$ 0.22	$ 0.22
Undistributed losses (in usd per share)		(0.09)	(0.05)	(0.14)	(0.13)
Total (in usd per share)		$ 0.02	$ 0.06	$ 0.08	$ 0.09
Distributed earnings		$ 3,375	$ 3,303	$ 6,745	$ 6,552
Undistributed losses		(2,722)	(1,645)	(4,172)	(3,810)
Total		$ 653	$ 1,658	$ 2,573	$ 2,742
Basic weighted average common shares outstanding (in shares)		30,667	29,787	30,592	29,618
Class B Common Shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Distributed earnings (in usd per share)		$ 0.11	$ 0.11	$ 0.22	$ 0.22
Undistributed losses (in usd per share)		(0.09)	(0.05)	(0.14)	(0.13)
Total (in usd per share)		$ 0.02	$ 0.06	$ 0.08	$ 0.09
Distributed earnings		$ 201	$ 202	$ 402	$ 403
Undistributed losses		(162)	(101)	(249)	(234)
Total		$ 39	$ 101	$ 153	$ 169
Basic weighted average common shares outstanding (in shares)		1,822	1,822	1,822	1,822

[1] Basic per share amounts are the same for Class A and Class B shares. Diluted per share amounts for Class A shares are shown above. Diluted earnings per share for Class B shares under the two-class method are $0.02 and $0.06 for the three months ended October 31, 2020 and 2019 and $0.09 and $0.10 for the six months ended October 31, 2020 and 2019. See Note E to the Condensed Consolidated Financial Statements.